Abstract: The aeolian sand belts are distributed extensively in Mainling great valley section of the Yarlung Zangbo River. Each belt can be divided into eroded area, erosion and deposition transition area, and deposition area by distinct aeolian sand activities. The two belts with aeolian sand activity were studied. The results show that sediments of the dune are mainly composed of fine sands with moderate sorting, fine skewness, and muti-modal grain size distribution. Grain size distribution on the surface of barchans can be attributed to the 'dune crest coarser’pattern as a whole with limited exception where grain size distribution shows a "finer crest" pattern. Spatial variations of grain size distribution among the barchans within the same aeolian sand belt were shown. Small barchans developed in the eroded area exhibit finer grain size, poor sorting, very fine skewness and multi-mode. In the erosion and deposition transition area and downwind deposition area, dune grain size becomes coarser with sorting better, fine skewness converting to nearly symmetry, and muti-mode grain size distribution pattern turning to be uni-mode.